bacteria have defenses against phages, including restriction enzymes that recognize and cut up certain phage DNA

what is a virulent phage?

a phage that reproduces only by the lytic cycle

describe the lytic cycle.

the lytic cycle is a phage reproductive cycle that culminates in hte death of the host cell. The lytic cycle produces new phages and digests the host's cell wall, releasing the progeny viruses

what are temperate phages?

these are phages that use both the lytic and lysogenic cycles

describe the lysogenic cycle

the lysogenic cycle replicates the phage genome without destroying the host. The viral DNA molecule is incorporated into the host cell's chromosome. Every time the host divides, it copies the phage DNA and passes the copies to daughter cells. An environmental signal can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode.

what is a prophage

viral DNA that is integrated in the host chromosome during the lytic cycle is called a prophage

where do viruses with viral envelopes get their envelopes from?

some viral envelopes are formed from the host cell's plasma membrane as the viral capsids exit. Other viral membranes form from the host's nucleear envelope and are then replaced by an envelope made from Golgi apparatus membrane

what do viral glycoproteins on viral envelopes do?

viral glycoproteins on the envelope bind to specific receptor molecules on the surface of a host cell

the broadest variety of RNA genomes is found in viruses that infect _______

animals

what is a provirus?

viruses with RNA genomes integrate their viral DNA into the host genome--this viral DNA is referred to as a provirus. Unlike the prophage, the provirus remains a permanent resident of the host cell. The host's RNA polymerase transcribes the proviral DNA into RNA molecules. The RNA molecules function both as mRNA for synthesis of viral proteins and as genomes for new virus particles released from the cell

viruses evolved from...

bits of cellular nucleic acid. candidates for the source of viral genomes are plasmids, circular DNA in bacteria and yeasts, and transposons, small mobile DNA segments. However, there is controversy about whether this virus evolved before or after cells.